Generally, soft errors involve changes to data, rather than changes to a physical circuit, where the data is unintentionally altered due to the presence of spurious changes in a circuit. A soft error, unlike many other errors, may be recoverable by rewriting the data or by other means. Soft errors may occur on transmission lines, in digital logic, in analog circuits, semiconductor storage elements and elsewhere.
Often times, soft errors are caused by neutrons from cosmic rays and alpha particles emitted from integrated circuit packaging material (soft error sources), although other causes are also possible. A neutron may undergo neutron capture by a nucleus of an atom, producing an unstable isotope that in turn decays producing a charged particle. A neutron may also collide with a lattice ion knocking it off. Both scenarios may lead to a charged particle traveling through the lattice. Radioactive decay of semiconductor packaging may also result in the emission of an alpha particle. These charged particles may deposit a trail of electron-hole pairs as they slow down. This deposited charge may then unpredictably alter a data state.
A latch or flip flop, both being storage elements, are fundamental building blocks of modern day processors, memory circuits, etc. Generally speaking, a latch or flip flop involves a circuit that stores a data value (e.g., a logic one or logic zero). In the case of alpha particles, where such a particle hits a transistor device in a storage element, a charge may be transferred to a sensitive node of the device that alters a data value stored in the device (the soft error). Clearly, an unintended data value alteration may result in improper operation of a circuit, processor, etc., employing the storage element. For example, a soft error may alter the program code stored in the memory of a microprocessor resulting in improper microprocessor operation. Such an error may be referred to as a soft error because the affected program code may be rewritten to restore proper microprocessor operation.
Accordingly, there is a need in the art for a storage circuit that does not alter a stored data value when alpha particles, neutrons, and other spurious changes, intrude on portions of the storage circuit. As will be recognized from the discussion below, these and other problems in the art are addressed by various systems and methods conforming to aspects of the present invention. Before explaining the disclosed embodiments in detail, it is to be understood that the invention is not limited in its application to the details of the particular arrangements shown, because the invention is capable of other embodiments. Moreover, aspects of the invention may be set forth in different combinations and arrangements to define inventions unique in their own right. Also, the terminology used herein is for the purpose of description and not of limitation.